Quality of gasoline, gas oil, or the like to be used as a fuel of an engine varies from region to region in the world, and an inferior fuel (e.g., gasoline or gas oil), a biofuel, or the like is used in some cases. A bearing to be arranged in a site that may be brought into contact with such fuel (e.g., in an electric fuel pump or an EGR valve) is required to have corrosion resistance against a sulfide and an organic acid contained in the inferior fuel or the biofuel.
Meanwhile, along with downsizing and lightweighting of the engine, the electric fuel pump or the like is also required to be downsized and lightweighted, and the bearing to be incorporated into the electric fuel pump or the like is also required to be downsized. For example, in the electric fuel pump, in order to achieve downsizing while securing discharge performance, the number of rotations needs to be increased. A bearing configured to support a shaft rotating at such high speed is required to have corrosion resistance and wear resistance (low-friction characteristic) as well as to be downsized.
For example, a copper-based sintered bearing is known as a bearing excellent in wear resistance. However, when the copper-based sintered bearing is brought into contact with the sulfide or the organic acid contained in the inferior fuel or the biofuel, its copper is liable to be corroded. For example, when the copper-based sintered bearing is brought into contact with the sulfide, there is a risk in that copper sulfide may be generated on a surface (in particular, a bearing surface) thereof to reduce a clearance between the bearing surface and a shaft, resulting in an increase in rotation torque. In addition, when the copper-based sintered bearing is brought into contact with the organic acid, its copper is eluted, and hence there is a risk in that its wear resistance may be lower, leading to a shorter product life. As described above, the copper-based sintered bearing is excellent in wear resistance, but is poor in corrosion resistance. Accordingly, the copper-based sintered bearing is not suited for an application in which the copper-based sintered bearing is brought into contact with the inferior fuel or the biofuel.
For example, in Patent Literature 1, there is disclosed an Al—Cu alloy-based sintered bearing. The Al—Cu alloy-based sintered bearing is excellent in sliding property, and is also excellent in corrosion resistance because an aluminum oxide film is generated on its surface.